Liquid level sensor

Abstract

A fuel sensing and monitoring apparatus and method is disclosed. The apparatus includes two spaced conductive coils constituting a primary and secondary winding of a transformer. A short coupling member is mounted to a movable member to which a float is attached, the float being located in the fuel tank of a vehicle. The float and movable member move in response to a change in fuel level in the tank. When the fuel level changes, the short coupling member moves relative to the primary and secondary windings. This movement adjusts or alters the transformer coupling between the primary and secondary and produces a variable output signal which can be correlated, through the use of appropriate circuitry, to a representation of the level or fuel in the tank as indicated by the position of the movable member to which the float is attached.

We claim: 
     
       1. A fuel level sensor comprising: a) an elongated probe adapted for insertion into a fuel container including side by side primary and secondary transformer coils wound around first and second coil forms insulated from contact with fuel in the fuel container by an elongated probe housing;   b) a fuel level float positioned within the fuel container for movement along a travel path as the fuel level changes with fuel consumption; said fuel level float including a coupling material that alters the transformer coupling between the primary and secondary transformer coils of said elongated probe as the fuel level float moves along the travel path; and   c) sensing circuitry for exciting the primary transformer coils with an excitation signal and evaluating a position of the fuel level float along said travel path from an output signal from the secondary transformer coil.   
     
     
       2. The fuel level sensor of claim 1 wherein the elongated probe housing forms a generally cylindrical housing and wherein the fuel level float is an annulus that fits over the cylindrical housing and moves along the cylindrical housing as the fuel level changes. 
     
     
       3. The fuel level sensor of claim 1 wherein the sensing circuitry comprises an alternating current source coupled to the primary transformer coils and an output monitoring circuit coupled to the secondary transformer coils and wherein both the alternating current source and the monitoring circuit are supported within a circuit housing positioned inside the fuel container. 
     
     
       4. The fuel level sensor of claim 1 wherein the winding density along the primary and/or secondary transformer coils is non-uniform to take into account the shape of the fuel container. 
     
     
       5. A fluid level sensor comprising: a) an elongated probe adapted for insertion into a fluid container including side by side primary and secondary transformer coils wound around first and second coil forms insulated from contact with fluid in the fluid container by an elongated probe housing;   b) a fluid level float positioned within the fluid container for movement along a travel path as the fluid level changes; said fluid level float including a coupling material that alters the transformer coupling between the primary and secondary transformer coils of said elongated probe as the fluid level float moves along the travel path; and   c) sensing circuitry for exciting the primary transformer coils with an excitation signal and evaluating a position of the fluid level float along said travel path from an output signal from the secondary transformer coil.   
     
     
       6. The fluid level sensor of claim 5 wherein the elongated probe housing forms a generally cylindrical housing and wherein the fluid level float is an annulus that fits over the cylindrical housing and moves along the cylindrical housing as the fluid level changes. 
     
     
       7. The fluid level sensor of claim 5 wherein the sensing circuitry comprises an alternating current source coupled to the primary transformer coils and an output monitoring circuit coupled to the secondary transformer coils and wherein both the alternating current source and the monitoring circuit are supported with an electronic housing positioned inside the fluid container. 
     
     
       8. The fluid level sensor of claim 5 wherein the winding density along the primary and/or secondary transformer coils is non-uniform to take into account the shape of the fuel container. 
     
     
       9. A fluid level sensor comprising: a) an elongated probe adapted for insertion into a fluid container including side by side primary and secondary transformer coils wound in a non-uniform density around first and second coil forms insulated from contact with fluid in the fluid container by an elongated probe housing, said elongated probe housing forming a generally cylindrical housing;   b) a fluid level float positioned within the fluid container for movement along a travel path as the fluid level changes wherein said fluid level float is an annulus that fits over the cylindrical housing and moves along the cylindrical housing as the fluid level changes, wherein said fluid level float also includes a coupling material that alters the transformer coupling between the primary and secondary transformer coils of said elongated probe as the fluid level float moves along the travel path; and   c) sensing circuitry for exciting the primary transformer coils with an excitation signal and evaluating a position of the fluid level float along said travel path from an output signal from the secondary transformer coil, wherein said sensing circuitry comprises an alternating current source coupled to the primary transformer coils and an output monitoring circuit coupled to the secondary transformer coils and wherein both the alternating current source and the monitoring circuit are supported within a circuit housing positioned inside the fluid container.   
     
     
       10. A fluid level sensor for measuring a volume of fluid in an irregularly shaped fluid container comprising: a) an elongated probe adapted for insertion into said fluid container including parallel spaced primary and secondary transformer coils insulated from contact with fluid in said fluid container by an elongated probe housing;   b) a fluid level float positioned within the fluid container for movement along a travel path as the fluid level changes; said fluid level float including a coupling material that alters the transformer coupling between the primary and secondary transformer coils of said elongated probe as the fluid level float moves along the travel path;   c) at least one of said primary and secondary coils having a nonlinear winding density corresponding to the shape of the fluid container along said travel path; and   d) sensing circuitry for exciting the primary transformer coils with an excitation signal and evaluating an output signal from the secondary transformer coil related to volume of fluid in the fluid container.   
     
     
       11. A fluid level sensor according to claim 10 wherein the primary and secondary coils are side by side. 
     
     
       12. A fluid level sensor for measuring a level of fluid in a fluid container comprising: a) an elongated probe adapted for insertion into said fluid container including parallel spaced primary and secondary transformer coils insulated from contact with fluid in said fluid container by an elongated probe housing;   b) a fluid level float positioned within the fluid container for movement along a travel path as the fluid level changes; said fluid level float including a coupling material that alters the transformer coupling between the primary and secondary transformer coils of said elongated probe as the fluid level float moves along the travel path;   c) said primary and secondary coils each comprising a continuous winding having a uniform sense; and   d) sensing circuitry for exciting the primary transformer coils with an excitation signal and evaluating a position of the fluid level float along said travel path from an output signal from the secondary transformer coil.   
     
     
       13. A fluid level sensor according to claim 12 wherein the primary and secondary coils are side by side.